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Numerical Simulations of Regional Wave Propagation in Realistic Earth Models,

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Preliminary results for numerical simulations of regional propagation in realistic earth models are presented. The modeling is motivated in part by three-component array observations which show that the P and S codas, and Lg wavetrains for regional sources are comprised of substantial amounts of forward scatteredmultipathed energy, and in part by results from numerical simulations of teleseismic wave propagation which suggest a correlation between the coda level and rate of decay and the aspect ratio of lithospheric heterogeneities. Numerical simulations are conducted using a two-dimensional, fourth order accurate, P-SV finite difference routine. The models consist of a heterogeneous layer over a homogeneous half-space. Perturbations are in velocity and parameterized using a gaussian correlation function. The wavefields generated using models containing high aspect ratio heterogeneities ANISO exhibit several characteristic consistent with regional array observations. First, the Pg wavetrain and coda consists of forward scattered, coherent plane wave energy trapped in the crustal waveguide. Models containing isotropic heterogeneities ISO inhibit the extent to which energy is trapped in the crustal waveguide and produce codas dominated by randomly scattered energy. Waveforms generated using models containing ANISO heterogeneities exhibit another feature commonly observed in regional array data. That is, that detailed features in waveforms observed at adjacent sensors exhibit a high degree of coherence, while those observed at sensors separated by distances on the order of a wavelength exhibit a somewhat surprising loss of coherence. Waveforms generated using models containing ISO heterogeneities exhibit a degree of incoherence inconsistent with regional array observations.

Subject Categories:

  • Government and Political Science
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons
  • Geology, Geochemistry and Mineralogy

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